The invention relates to an article of footwear and in particular to a method for attachment and detachment of a footwear upper to a lower outsole.
Known footwear constructions methods, in particular leisure footwear, include two main components: 1) a formed outsole design with a generalized foot print shape to protect the bottom of a foot; and 2) an upper made with flexible material to cover, protect and secure the foot to the outsole. The outsole is typically made from a molded construction using urethane rubber and elastic polymers alike to serve as ground engaging surface for the footwear. The outsole can also provide cushioning, support while insulating the foot from impacts during a gait cycle. The outsole can be flexible and bendable but generally are not stretchable. The footwear upper is constructed out of layered materials such as leather, canvas, suede, fabric or combinations of natural and synthetic materials. These materials are utilized primarily for style while maintaining protection of the foot. Often the materials used are less flexible, breathable and can be hard and none pliable. In construction, the two main components are permanently bonded together in creating the footwear. A mid sole and sock liner are often used on top of the outsole to provide additional cushioning and support needs of the foot.
In a typical footwear construction, the footwear's shape or footprint is determined by the outsole design. In most instances general assumptions are made in creating an outline perimeter shape to accommodate all foot shapes. This shape also determines the fit of the fore foot and mid foot as the footwear upper is bound to the entire perimeters of the outsole. Since most footwear upper construction utilizes non-stretchable materials, lacing and/or elastic material is used to achieve proper fit in securing the footwear to the foot. The foot is first strapped in, then presses down into the sole as lacing is tightened to secure the foot. This method of adjustment no doubt creates uneven pressure points along the entire fore and mid foot region while in static or in motion. The conventional method of constructing footwear may lead to discomfort and fit issues due to the unique shapes and sizes of everyone's foot. A generalized footwear shape can fit differently on each wearer's foot having an equal overall shoe size. It can be difficult to create footwear to fit every foot shape the same way. The inflexibility of the footwear due to construction and use of materials can further attribute to the problem of fit and discomfort.
During a gait cycle, the biomechanical movements changes the external shapes of the foot as weight is being applied. This effects in particular, forefoot and mid foot region as it pronates to distribute body weight. In the push off stage of the gait cycle, the forefoot region bends in dorsiflexion and creates a folding compression tension onto the upper's forefoot areas. The binding compression effects are then transferred onto the top of the forefoot's toe area causing discomfort with each step. This binding effect is due to overly ridged upper material used on the upper and the bonding of upper to the perimeters of the outsole. The pronatory forefoot flexing movement can further compound the footwear discomfort level as the foot's natural motions are met with resistance within the footwear. This resistance also comes from the upper bound to the outsole's perimeter shapes restricting the forefoot's flexion and expansion movements.
Due to each wearer's unique foot shape, a better way of securing the upper to the lower is needed to address fit, comfort, and minimize pressure points to our feet.
Further, the upper's purpose is to cover and protect a wearer's foot. But more importantly in the eyes of the consumer, it is the style, color and design that matters most over the purchase decision. With the outsole bonded to the upper, the footwear is limited to just one style.
Numerous attempts have been made in the past to provide footwear having detachable upper construction, however, these detachable footwear systems reflect the typical footwear construction method described above, as the upper are still bound to the perimeter shape of the outsole. The prior inventions achieve detachability of the upper to the outsole by adding features where the upper and the outsole meets. The examples can be seen in US Patent Publication No. US2010/0024251A1 where loops are added along the upper's perimeter to capture the lower. Zipper systems are also used to combine the upper to the outsole in U.S. Pat. No. 4,103,440 and US Patent Publication No. 2008/0235992. Attachment elements are used in US Patent Publication No. 2005/0097781, U.S. Pat. Nos. 8,230,621B2 and 6,349,486B1 to secure the upper to the outsole. A complete upper footwear assembly with formed locking features along its mid sole perimeters to interlock with the outsole is shown in U.S. Pat. Nos. 5,083,385, 4,267,650, and 3,878,626. An outer sole with straps to stretch over the inner sole is described in U.S. Pat. No. 7,591,084. One of the earlier inventions pertaining to a detachable upper can be seen in U.S. Pat. No. 2,438,711A as the upper and lower are combined by lace looping through its perimeter base.
Thus, many novel ways of combining the upper to the lower outsole have been discloses. However, the prior art does not address the limiting effects on the foot's natural movements with an upper bound to the perimeter of the outsole shape. Furthermore, the prior art does not acknowledge a way of securing the footwear to the foot without causing uneven pressure points or binding as the foot moves through the biomechanical movements of a gait cycle.
In typical construction, the outsoles and mid soles more often are made flat, overly ridged and less flexible. The overall focus is on manufacturing process and style rather than comfort or function. The flat layers of mid soles and outsoles are easy to produce but offers inadequate cushion for many regions of the foot. These soles provides a flat cushioning bed on which the foot's contour will rest on. The inability for the sole to emulate foot's bottom contours hinders its natural biomechanical movement in a gait cycle. During a gait cycle the foot performs a trilateral movement known as pronation and supenation. Pronation is a compression state when weight is being transferred to the foot. Supenation is a rebound state for the foot to decompress and return to its natural state. Current production footwear outsole serves only as a stationary platform for the these movements and not as a system to enhance the movements of the foot. To require the outsole to flex and bend with the foot a thinner and more ergonomically designed outsole and mid-sole system is needed to hug the bottom contours of the foot.
The mid sole are typically made flat and of single density polyurethane foam such as Ethylene-Vinyl Acetate (EVA) and the like along the entire bottom sole surface. Such mid sole serves as the main cushioning and support mechanism for the footwear. While this is an economical and practical way of constructing a mid sole, it often overlooks the functional and longevity needs of a mid sole design. EVA foam deteriorates quickly with wear over time, with a designed life span lasting less than 6 months.
Different parts of the foot have unique cushioning and support needs driven by the bone structures and biomechanical motion of the foot. The rear of the foot, known as the heel, contains the Calcaneus bone structure which serves as the main load bearing base of the foot when in motion or at rest. The heel also provides the initial landing or strike during a gait cycle as part of our bi-pedal movement. As the heel strikes the ground, the heels may be subjected to the entire weight of our body. During running, jumping and other athletic sports activities, the heel strike may far exceeds one's own body weight. Thus a resilient, more energy absorbent and elastic material may be needed at the heel area.
The mid foot consists of a key-stone like structure with the Navicular, Cuboids, and Cuneiform bones. The mid foot also houses the Tarsometatarsal joint which serves as a connection to the first though fifth Metatarsal bones. The mid foot is also known as the medial and lateral arches of the foot. The mid foot joint structure serves as a compressible arch to allow flexibility. Flexing of the arch serves as a suspension system to absorb the load of the foot in compression and rebound. This trilateral motion is described as pronation and supenation during a gait cycle. Due to the biomechanical nature of mid foot, support is a much needed element to incorporate into the mid-sole's medial and lateral arch design.
The forefoot is located at the ends of the metatarsal bone as it connects to the phalanges also known as toes. At the joints of the phalanges and the first Metatarsal joint lies the Sesamoid bone. The Sesamoid bone with the ends of the first Metatarsal are also know as the ball of the foot. The ball of the foot serves as another load bearing zone as weight of the body is distributed onto the fore foot and the rear foot. The forefoot is also responsible for landing, weight distribution, and propulsion as the foot rolls forward to begin the pushing off the stage of the gait cycle. This unique fore foot zone may also require materials to be resilient, more energy absorbent and elastic that are unique from the needs of mid foot.
The outsole design in most footwear serves as one semi ridged flat platform to support the entire foot. In particular the rear heel area of the outsole is typically made flat with squared off edges different from the natural round shape of our heel. These edges or pads extend outward adding to the overall rear foot footprint area for balance, stability and weight distribution. This method of expanding heel support can be seen from the rear and the bottom of most sneakers and leisure footwear. While this design approach is warranted in some applications, not all footwear benefits from such a design. In some instances it may cause more injuries for the user. Injuries may result as the expanded heel support unknowingly lands or catches on an uneven or offset surfaces such as a steps or the sidewalk. By landing on an uneven surface, this causes the extended flat heel section to tilt as the foot tries to compensate and find its level. This translates into lost of balance or a quick twisting motion as our ankle is forced to move with the footwear. When twisting of the ankle joint exceeds the limitation of the ankle, flex injury may result in forms of a sprained ankle. A thinner and flexible rounded shape to closely mimic and surrounds our heel contours may be needed for the outsole design. This type of outsole design will allow the forefoot and mid foot to move and flex as it adapts to the uneven surface. The external round heel section allows the heel to slide down from the uneven surface rather then forcing the entire foot and ankle to twist as whole.
Current indoor footwear market consists mainly of foam padded slippers, moccasins, and loafers. Known padded slippers generally utilize low density foam for cushioning and padding. The foam used is often of low density and offers only short term general cushioning as it loses its deflection and rebound quickly. The slipper are made to loosely fit the foot as they are made oversized to accommodate many different foot shapes. This causes the user to constantly maneuver one's foot in trying to keep their slippers on their feet while sitting or walking. Indoor footwear often does not provide contours formed into the soles to properly support and cushion the foot. The padded slippers, moccasins and loafers can be overly insulated without proper ventilation causing overheating and foot sweat. While some indoor footwear are made to be washable, they are difficult to dry due to the thick foam padding bound to the rubber outsole. Sanitary odor of these footwear may also be of concern.
Socks are often a preferred choice for indoor use due to the light and comfortable natures of its construction, as they are easy to wash and dried. Some socks are marketed for indoor use by adding molded rubber textures on the sole for traction against smooth slippery floor surfaces. Socks are comfortable to wear as they generally do not have pressure points exerted onto the foot. The stretchable body of the socks easily conforms to the wearer's unique foot shapes and stay on the foot without adjustment. The light and breathable nature of the materials offer just enough protection and insulation for indoors use, while offering a variety of styles and designs to suit the taste of the wearer. However, known socks provide almost no cushioning and support for the foot. The foot can still be subjected to shocks and impacts forces from walking on hard ground surfaces. Wear and tear is also major issue for socks as woven material being subject to high pressure and friction. The wear is compounded when used over more abrasive floor surfaces like concrete, tile and wood. Typically the life cycle of an indoor sock can be short as the heel and forefoot wears at a quicker pace. Although inexpensive to produce and purchase, overtime the cost may compound.